Abstract

This document specifies the WOFF font packaging format.
This format was designed to provide lightweight, easy-to-implement compression of font data,
suitable for use with CSS @font-face rules.
Any properly licensed TrueType/OpenType/Open Font Format file can be packaged in WOFF format for Web use.
User agents decode the WOFF file to restore the font data such that it will display identically to the input font.

The WOFF format also allows additional metadata to be attached to the file;
this can be used by font designers or vendors to include licensing or other information,
beyond that present in the original font.
Such metadata does not affect the rendering of the font in any way,
but may be displayed to the user on request.

The WOFF format is not intended to replace other formats
such as TrueType/OpenType/Open Font Format or SVG fonts,
but provides an alternative solution for use cases where these formats may be less optimal,
or where licensing considerations make their use less acceptable.

Status of This Document

This section describes the status of this document at the
time of its publication. Other documents may supersede this
document. A list of current W3C publications and the latest
revision of this technical report can be found in the W3C technical reports index at
http://www.w3.org/TR/.

This is the W3C Recommendation of "WOFF File Format 1.0". This document has been reviewed by W3C Members, by software developers, and by other W3C groups and interested parties, and is endorsed by the Director as a W3C Recommendation. It is a stable document and may be used as reference material or cited from another document. W3C's role in making the Recommendation is to draw attention to the specification and to promote its widespread deployment. This enhances the functionality and interoperability of the Web.

Sufficient reports of implementation experience have been gathered to demonstrate that the “WOFF File Format 1.0” syntax and features are implementable and are interpreted in a consistent manner. To do so, the Working Group would insure that all features have been implemented in at least two implementation in an interoperable way.

1. Introduction

This document specifies a simple compressed file format for fonts, designed
primarily for use on the Web and known as WOFF (Web Open Font Format).
Despite this name, WOFF should be regarded as a container format
or "wrapper" for font data in already-existing formats
rather than an actual font format in its own right.

The WOFF format is a container for the table-based sfnt structure used in e.g. TrueType [TrueType], OpenType [OpenType] and Open Font Format [OFF] fonts, hereafter referred to as sfnt fonts.
A WOFF file is simply a repackaged
version of a sfnt font with optional compression of the font data tables.
The WOFF file format also allows font metadata and private-use data to be
included separately from the font data. WOFF encoding tools convert an input
sfnt font into a WOFF formatted file, and user agents restore the
sfnt font data for use with a Web document.

The structure and contents of decoded font data exactly match
those of a well-formed input font file. Tools producing WOFF files may provide other
font editing features such as glyph subsetting, validation or font feature
additions but these are considered outside the scope of this format. Independent
of these features, both tools and user agents are expected to assure that the validity of
the underlying font data is preserved.

Notational Conventions

The all-uppercase key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
"SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be
interpreted as described in RFC 2119 [RFC-2119].
If these words occur in lower- or mixed case, they should be interpreted
in accordance with their normal English meaning.

This document includes sections of text that are called out as "Notes"
and set off from the main text of the specification.
These notes are intended as informative explanations or clarifications,
to serve as hints or guides to implementers and users,
but are not part of the normative text.

2. General Requirements

The primary purpose of the WOFF format is to package fonts linked to Web documents
by means of CSS @font-face rules.
User agents supporting the WOFF file format for linked fonts must respect
the requirements of the CSS3 Fonts specification ([CSS3-Fonts] Section 4.1:
The @font-face rule). In particular,
such linked fonts are only available to the documents that reference them;
they MUST NOT be made available to other applications or documents on the user's system.

The WOFF format is intended for use with @font-face
to provide fonts linked to specific Web documents.
Therefore, WOFF files must not be treated as an installable font format
in desktop operating systems or similar environments.
The WOFF-packaged data will typically be decoded to sfnt format
for use by existing font-rendering APIs that expect OpenType font data,
but such decoded font must not be exposed to other documents or applications.

3. Overall File Structure

The structure of WOFF files is similar to the structure of sfnt fonts:
a table directory containing lengths and offsets to individual font data tables,
followed by the data tables themselves. The sfnt structure is described fully in
the TrueType [TrueType], OpenType [OpenType] and Open Font Format [OFF] specifications.

The main body of the file consists of the same collection of font data tables
as the input sfnt font, stored in the same order, except
that each table MAY be compressed, and the sfnt table directory is replaced by
the WOFF table directory.

The WOFF specification does not guarantee that the actual font data
packaged in a valid WOFF container is in fact correct and usable.
It requires only that the WOFF packaging structure—header, table directory,
and compressed tables—conforms to this specification.
The contained data must be used with just as much caution as font data
delivered in "raw" form or via any other packaging method.

A complete WOFF file consists of several blocks: a 44-byte header,
immediately followed (in this order) by a variable-size table directory,
a variable number of font tables, an optional block of extended
metadata, and an optional block of private data.
Except for padding with a maximum of three null bytes
in places where 4-byte alignment of a table length
or block offset is specified,
there MUST NOT be any extraneous data between the data blocks
or font data tables indicated by the WOFF header and table directory,
or beyond the last such block or table.
If such extraneous data is present a conforming user agent
MUST reject the file as invalid.
The file MUST also be rejected as invalid
if the offsets and lengths of any data blocks or font tables
indicate overlapping byte ranges of the file,
or ranges that would extend beyond the end of the file.

WOFF File

WOFFHeader

File header with basic font type and version, along
with offsets to metadata and private data blocks.

TableDirectory

Directory of font tables, indicating the original
size, compressed size and location of each table within the WOFF file.

An optional block of extended metadata,
represented in XML format and compressed for storage in the WOFF file.

PrivateData

An optional block of private data for the font
designer, foundry, or vendor to use.

Data values stored in the WOFF Header and WOFF Table Directory sections are
stored in big-endian format, just as values are within sfnt fonts. The
following basic data types are used in the description:

Data types

UInt32

32-bit (4-byte) unsigned integer in big-endian
format

UInt16

16-bit (2-byte) unsigned integer in big-endian
format

All sizes and offsets described in this document are assumed to be in bytes unless
otherwise noted.

4. WOFF Header

The header includes an identifying signature and indicates the specific kind
of font data included in the file (TrueType or CFF outline data); it also has a
font version number, offsets to additional data chunks, and the number of
entries in the table directory that immediately follows the header:

WOFFHeader

UInt32

signature

0x774F4646 'wOFF'

UInt32

flavor

The "sfnt version" of the input font.

UInt32

length

Total size of the WOFF file.

UInt16

numTables

Number of entries in directory of font
tables.

UInt16

reserved

Reserved; set to zero.

UInt32

totalSfntSize

Total size needed for the
uncompressed font data, including the sfnt header, directory,
and font tables (including padding).

UInt16

majorVersion

Major version of the WOFF
file.

UInt16

minorVersion

Minor version of the WOFF
file.

UInt32

metaOffset

Offset to metadata block, from
beginning of WOFF file.

UInt32

metaLength

Length of compressed metadata block.

UInt32

metaOrigLength

Uncompressed size of metadata
block.

UInt32

privOffset

Offset to private data block, from
beginning of WOFF file.

UInt32

privLength

Length of private data block.

The signature field in the WOFF header
MUST contain the "magic number" 0x774F4646.
If the field does not contain this value,
user agents MUST reject the file as invalid.

The flavor field corresponds to the "sfnt version"
field found at the beginning of an sfnt file,
indicating the type of font data contained.
Although only fonts of type 0x00010000 (the version number 1.0
as a 16.16 fixed-point value, indicating TrueType glyph data)
and 0x4F54544F (the tag 'OTTO', indicating CFF glyph data)
are widely supported at present, it is not an error in the WOFF file if the
flavor field contains a different value, indicating a
WOFF-packaged version of a different sfnt flavor. (The value 0x74727565 'true'
has been used for some TrueType-flavored fonts on Mac
OS, for example.) Whether client software will actually support other types of
sfnt font data is outside the scope of the WOFF specification, which
simply describes how the sfnt is repackaged for Web use.

The WOFF majorVersion and minorVersion fields specify the version number for a given
WOFF file, which can be based on the version number of the input font but is
not required to be. These fields have no effect on font loading or usage
behavior in user agents.

The totalSfntSize field is the sum of the
uncompressed font table sizes, each padded to a multiple of 4 bytes, plus
the size of the sfnt header and table directory. Thus, this is the size of
buffer needed to decode the complete WOFF-packaged font (but not metadata,
which is not part of the input sfnt file) into a standard sfnt structure.
This value MUST be a multiple of 4, because all font tables
including the last are to be padded to a 4-byte boundary.
If this value
is incorrect, a conforming user agent MUST reject the file as invalid.

The sfnt header includes three fields (searchRange,
entrySelector and rangeShift) that are designed to
facilitate a binary search of the table directory.
As the proper value for each of these fields can be computed directly
from the number of font tables, they are not stored in the WOFF file.
User agents that decode WOFF files back to an sfnt structure
MUST therefore compute the correct values for these fields in the sfnt header,
as described in the OpenType/OFF specification.[OFF]

The correct value for totalSfntSize may be computed
as illustrated by the following pseudo-code:

If either or both of the metadata or private blocks is not present,
the relevant offset and length fields MUST be set to zero.
If the metadata or private data offset and length fields indicate byte
ranges that overlap other data blocks or tables,
or extend beyond the end of the file,
a conforming user agent MUST reject the file as invalid.

The header includes a reserved field; this MUST be
set to zero. If this field is non-zero, a conforming user agent
MUST reject the file as invalid.

5. Table Directory

The table directory is an array of WOFF table directory entries, as defined
below. The directory follows immediately after the WOFF file header; therefore,
there is no explicit offset in the header pointing to this block. Its size is
calculated by multiplying the numTables value in the
WOFF header times the size of a single WOFF table directory. Each table
directory entry specifies the size and location of a single font data table.

WOFF TableDirectoryEntry

UInt32

tag

4-byte sfnt table identifier.

UInt32

offset

Offset to the data, from beginning of WOFF
file.

UInt32

compLength

Length of the compressed data,
excluding padding.

UInt32

origLength

Length of the uncompressed table,
excluding padding.

UInt32

origChecksum

Checksum of the uncompressed
table.

The format of tag values are defined by the
specifications for sfnt fonts. The offset and
compLength fields identify the location of the
compressed font table. The origLength and origCheckSum
fields are the length and checksum of the
input font table from the table directory of the input
font.

The sfnt format specifications require that font tables be aligned on
4-byte boundaries. Font tables whose length is not a multiple of 4 are padded
with null bytes up to the next 4-byte boundary. Font data tables in the WOFF
file have the same requirement: they MUST begin on 4-byte boundaries and be
zero-padded to the next 4-byte boundary. The compLength and origLength fields
in the table directory store the exact, unpadded length.

If the offset and compLength values
indicate a byte range that overlaps
other data blocks or font tables, or if the byte range extends beyond
the end of the file, a conforming user agent MUST reject the file as
invalid.

If the length of a compressed font table would be the same as or greater than
the length of the input font table, the font table MUST be stored
uncompressed in the WOFF file and the compLength set
equal to the origLength. Tools MAY also opt to leave
other tables uncompressed (e.g. all tables less than a certain size), in which
case compLength will be equal to origLength for these tables as well.
WOFF files containing
table directory entries for which compLength is
greater than origLength are considered invalid and
MUST NOT be loaded by user agents. Files containing compressed font tables that
decompress to a size other than origLength are also
considered invalid and MUST NOT be loaded.

The sfnt font specifications require that table directory entries
are sorted in ascending order of tag value. To
simplify processing, WOFF-producing tools MUST produce a table directory with
entries in ascending tag value order. User agents MUST
likewise assure that the sfnt table directory is recreated in ascending
tag order when restoring the font data to its uncompressed
state. The ordering of the font tables themselves is independent of the order of
directory entries, as described below.

sfnt fonts store a checksum for each table in the table directory, and
an overall checksum for the entire font in the head
table (see the TrueType, OpenType or Open Font Format specifications for the
definition of each calculation). Tools producing WOFF files MUST validate these
checksums, and reject the font if errors are found.

A WOFF file contains the same set of font tables as the input font
from which it was created. This means that the overall font checksum of a
font decompressed from a conformant WOFF file will always match the checksum
in the well-formed input font. In the case where the
input font included unreferenced data between or after the actual tables,
this would affect the overall checksum of the input font, but would be
dropped during creation of the WOFF file.

A well-formed input font does not have structural anomalies such as
incorrect padding, overlapping font tables,
extraneous data between tables (which will be discarded by the WOFF
generator), or incorrect checksums.

To ensure that lossless round-trip conversion from sfnt to WOFF and back
will be possible, a well-formed input font should conform
to certain norms that are not
strictly required by the OpenType/OFF specification, although they are common
practice:

Font table padding

The OpenType/OFF specification is not entirely clear about whether all
tables in an sfnt font must be padded with 0-3 zero bytes to a multiple
of 4 bytes in length, or whether this applies only between tables,
and the final table of the file may be left unpadded.
Most current tools and fonts seem to expect all tables to be padded to a 4-byte
boundary, including the last.
The WOFF specification assumes this behavior, and specifies that the
totalSfntLength field in the WOFF header provides for such padding.
To ensure that a given font can be packaged as a WOFF file and then decoded
to its original format and give a byte-for-byte identical result,
the input font should therefore be padded to a multiple of 4 bytes in length.

No "hidden" data

The OpenType/OFF specification does not explicitly prohibit the
presence of "extra" data or padding in between the font tables;
as the table directory includes the offset and length of each actual table,
such data would simply be ignored. However, the WOFF format makes no
provision to preserve such non-font-table data when packaging a font,
and therefore it would not survive a round-trip format conversion.

Header fields are correct

The OpenType/OFF header fields (searchRange,
entrySelector, rangeShift)
that are designed to facilitate a binary search of the table directory
must be correct in the input sfnt file,
as the WOFF format does not directly preserve these fields
but assumes a WOFF decoder will recompute them as needed.

Checksums are correct

The WOFF specification says that table checksums must be validated
(and corrected if necessary) by WOFF creators.
In order for complete
round-trip fidelity, therefore, the checksums in the input sfnt file
must also be correct prior to WOFF packaging.

No overlapping tables

The offset and length values in the input sfnt table directory must not indicate overlapping byte ranges of the input font.

The result of creating a WOFF file and then decoding this to
regenerate an sfnt font MUST result in a final font that is bitwise-identical to
the well-formed input font..
If the input font has defects or anomalies
that make this impossible,
the WOFF-generating tool SHOULD either reject the font
or issue an appropriate warning
that lossless round-trip conversion will not be possible.

6. Font Data Tables

The font data tables in the WOFF file are exactly the same as the tables in
the input font, except that each table MAY have been
compressed. If compressed, it MUST have been compressed by the compress2() function of zlib [Compress2] (or an
equivalent, compatible algorithm). User agents use the
uncompress() function of zlib [Uncompress](or an
equivalent, compatible algorithm)
to decompress each table.
The underlying format these functions use is described in the ZLIB
specification [ZLib]. User agents or other programs that decode WOFF files MUST be able to handle
tables that have been compressed.
If the
decompression function fails for any table, the WOFF file is invalid
and MUST NOT be loaded.

The font data tables MUST be stored immediately following the table
directory, without gaps except for any padding that is required (up to three
null bytes at the end of each table) to ensure 4-byte alignment.

Font tables in WOFF files MUST be stored in the same order as the well-formed input font.
The table order is implied by offset values in the table directory; sorting table
directory entries into ascending offset value order
produces a list of entries in an order equivalent to that of the font tables.

User agents need not necessarily reconstitute the input font as a whole, and may reorder tables when decoding the WOFF file to sfnt form; they may access individual tables directly as needed. Under these circumstances the resulting sfnt will no longer be an exact copy of the input font, and checksums or digital signature data may be invalidated as a result.

In some cases, sites deploying WOFF files as Web fonts may wish to subset the character
repertoire, optimize table ordering for efficient text layout or rasterization,
or remove (or add) optional font tables depending on the particular features needed for a site.
User agents might make similar modifications to the font during decoding,
such as omitting tables that are not needed by their particular text display system.

The automatic removal of OpenType features such as GPOS and GSUB information
at any stage in the process of deploying a WOFF file is strongly discouraged.
Many writing systems around the world rely on these features
for very basic display of text in the script that they use.

If either a WOFF-creation tool or a WOFF-consuming user agent
reorders or otherwise modifies the collection of font tables,
the font checksum in the head table will need to be recalculated
as it will be affected by the changed offsets in
the sfnt table directory.
Any DSIG table in the input font will also be invalidated by such changes, and should therefore be removed from the modified font.
A new signature could be added to the modified font,
as described by the OpenType and Open Font Format specifications
(if appropriate signing credentials are available to the tool involved).
Any such pre- and/or post-processing
represents a modification of the font data being packaged;
while it might be done in conjunction with WOFF packaging for Web deployment,
it falls outside the scope of the WOFF specification.

The OpenType/OFF specification does not explicitly prohibit the
presence of "extra" data or padding in between the font tables in the sfnt format;
as the table directory includes the offset and length of each actual table,
such data would simply be ignored. However, the WOFF format makes no
provision to preserve such "hidden" non-font-table data when packaging a font,
and therefore it would not survive a round-trip format conversion.

7. Extended Metadata Block

The WOFF file MAY include a block of extended metadata. This may be more extensive and more easily accesible than metadata present in sfnt tables. The metadata block consists of XML data compressed by
zlib; the file header specifies both the size of the actual compressed and the
original uncompressed size in order to facilitate memory allocation.

The presence (or absence) and content of the metadata block
MUST NOT affect font loading or rendering behavior of user agents;
it is intended to be purely informative.
User agents MAY provide a means for users to view information about fonts
(such as a "Font Information" panel). If such information is provided,
then they MUST treat the metadata block as the primary source,
and MAY fall back to presenting information from the font's name
table entries when relevant extended metadata elements are not present.

If present, the metadata MUST be compressed; it is never stored in
uncompressed form.

The metadata block MUST follow immediately after the last font table. As all font
data tables are padded with up to three null bytes
if needed to reach a 4-byte boundary,
the beginning of the metadata block will always be 4-byte aligned.
If the metadata block is the last block in the WOFF file,
there SHOULD be no additional padding after the end of the block.

The extended metadata MUST be well-formed XMLencoded in UTF-8.

The schema for the extended metadata XML is described below.
If the extended metadata does not match this schema,
it is invalid.
It is also invalid if it cannot be decompressed
by zlib's uncompress() function (or equivalent),
or if the length of the decompressed data does not match the metaOrigLength value specified in the WOFF header.
Thus, valid metadata is well formed, conforms to the schema below,
and is stored in compressed form in the WOFF file.
A conforming user agent MUST ignore an invalid metadata block,
as if the block were not present.

This description is also available
as a RelaxNG schema.
In the event of a discrepancy between the RelaxNG schema
and the text of the specification, the text takes precedence.

Several elements store their data in text
child elements; this is to support localization. The text
elements MAY be given a lang attribute
in the XML namespace [XML].
For backwards compatibility, lang attributes in the default namepsace
are also accepted in older content, and SHOULD be treated the same
as xml:lang.
New content SHOULD instead use xml:lang.

The syntax of values of the xml:lang attribute can be found in
BCP47 [BCP47].
A user agent displaying metadata SHOULD choose a preferred language/locale to display from among those available, following BCP47.

The user agent SHOULD choose which of the available text
elements to display as follows:

If a text element is available that matches the user's
preferred language, as determined via
an explicit preference or implied by the current locale, use this language.

If the user agent has a concept of a list of "acceptable" languages or
defaults, try each of these in turn and use the first one for which a match found.

If there is a text element with no xml:lang
attribute, use this; in the event that more than one exists, use the first of them.

If no match is found yet, use the first text element.
(Thus, the metadata creator can determine the "localization of last resort"
simply by choosing which language to put first in each group of
text elements.)

Such localizable elements are
indicated by the statement
"This element may be localized using text child elements"
in the description below;
the internal structure of text elements with
xml:lang attributes is not repeated for each element
type.
In each of these localizable elements,
at least one
text child element MUST be present,
except in the case of the license element (as described below).

metadata element

The main element. This element is REQUIRED.

attributes

version

A version number indicating the format version of the
metadata element. This is currently 1.0.
This attribute is REQUIRED.

children

uniqueid

Zero or one child elements

vendor

Zero or one child elements

credits

Zero or one child elements

description

Zero or one child elements

license

Zero or one child elements

copyright

Zero or one child elements

trademark

Zero or one child elements

licensee

Zero or one child elements

extension

Zero or more child elements

All first-level child elements of the metadata are OPTIONAL, and may occur in
any order as children of the top-level metadata
element.

The extension element is intended to allow
vendors to include metadata that is not covered by the specific elements
defined here, while following a standard model. User agents that provide a means
for the user to view WOFF file metadata SHOULD include such
extension elements in the metadata presented to the user.

uniqueid element

A unique identifier string for the font. This element is recommended, but not
required for the metadata to be valid. This element MUST be a child of the
metadata element. This is an empty element.

attributes

id

The identification string. This attribute is REQUIRED.

The string defined in the uniqueid element is not
guaranteed to be truly unique, as there is no central registry or authority to
ensure this, but it is intended to allow vendors to reliably identify the exact
version of a particular font. The use of "reverse-DNS" prefixes to provide a
"namespace" is recommended; this can be augmented by additional identification
data of the vendor's own design.

The id attribute of the uniqueid element,
and of several further metadata elements defined below,
is not required to conform to the rules for the XML type ID;
its form is at the discretion of the font creator or vendor.

vendor element

Information about the font vendor. This element is recommended, but not
required for the metadata to be valid. This element MUST be a child of the
metadata element. This is an empty element.

attributes

name

The name of the font vendor. This attribute is REQUIRED.

url

The url for the font vendor. This attribute is
OPTIONAL.

dir

The text direction, either ltr (for "left to right") or rtl (for "right to left").
This attribute is OPTIONAL and, if omitted, defaults to ltr.

class

An arbitrary set of space-separated tokens.
This attribute is OPTIONAL.

credits element

Credit information for the font. This can include any type of credit the
vendor desires: designer, hinter, and so on. This element is OPTIONAL. If
present, it MUST be a child of the metadata element
and it MUST contain at least one credit element. This
element has no attributes.

children

credit

One or more child elements

credit element

A single credit record. If present, it MUST be a child of the
credits element. This is an empty element.

attributes

name

The name of the entity being credited. This attribute is REQUIRED.

url

The url for the entity being credited. This attribute is
OPTIONAL.

role

The role of the entity being credited. This attribute is
OPTIONAL.

dir

The text direction, either ltr (for "left to right") or rtl (for "right to left").
This attribute is OPTIONAL and, if omitted, defaults to ltr.

class

An arbitrary set of space-separated tokens.
This attribute is OPTIONAL.

description element

An arbitrary text description of the font's design, its history, etc. This
element is OPTIONAL. If present, it MUST be a child of the metadata element.
This element may be localized using text child elements.

attributes

url

The url for more information about the font design, history, etc. This attribute is OPTIONAL.

children

text

One or more child elements containing character data and optionally div and/or span children

license element

Licensing information for the font.
This element is OPTIONAL. If present, it MUST be a
child of the metadata element.
This element may be localized using text child elements;
however, it is permitted to be empty (for example, if the vendor
prefers to just provide a license URL rather than including the actual
text of the license.)

attributes

url

The url for the license, more information about the license,
etc. This attribute is OPTIONAL.

id

An identifying string for the license. This attribute is
OPTIONAL.

children

text

Zero or more child elements containing character data and optionally div and/or span children

copyright element

The copyright for the font. This element is OPTIONAL. If present, it MUST be
a child of the metadata element.
This element may be localized using text child elements.
This element has no attributes.

children

text

One or more child elements containing character data and optionally div and/or span children

trademark element

The trademark for the font. This element is OPTIONAL. If present, it MUST be
a child of the metadata element.
This element may be localized using text child elements.
This element has no attributes.

children

text

One or more child elements containing character data and optionally div and/or span children

licensee element

The licensee of the font. This element is OPTIONAL. If present, it MUST be a
child of the metadata element. This is an empty
element.

attributes

name

The name of the licensee. This attribute is REQUIRED.

dir

The text direction, either ltr (for "left to right") or rtl (for "right to left").
This attribute is OPTIONAL and, if omitted, defaults to ltr.

class

An arbitrary set of space-separated tokens.
This attribute is OPTIONAL.

Although the metadata elements and structure defined above
are expected to be sufficient for most needs,
an extension mechanism is also provided so that font vendors
can include arbitrary metadata items that do not fit
the standard elements above:

extension element

A container element for extended metadata provided by the vendor. Zero or more
extension elements may be present as children of
the top-level metadata element. Each such
metadata extension has an optional name,
which may be provided in multiple languages,
and one or more item elements.

attributes

id

An arbitrary identifier defined by the vendor.
This attribute is OPTIONAL.

children

name

Zero or more child elements

item

One or more child elements

item element

At least one item element MUST be present in
each extension container.

attributes

id

An arbitrary identifier defined by the vendor.
This attribute is OPTIONAL.

children

name

One or more child elements

value

One or more child elements

name element

Zero or more name elements may be used to provide
a human-friendly name for the collection of extended metadata items
in an extension element.
A user agent
that displays metadata SHOULD choose the name with most the appropriate language
from among those available for each named extension element.
This child element is OPTIONAL in extension elements;
anonymous extension elements are also permissible.

One or more name elements are also used to provide
a human-friendly name for a specific extended metadata item. A user agent
that displays metadata SHOULD choose the name with the most appropriate language from
among those available for each item element.
This child element is REQUIRED in item elements;
an item element with no
name is invalid and SHOULD be ignored.

attributes

xml:lang

A language tag as defined in BCP47 [BCP47].
This attribute is OPTIONAL.

dir

The text direction, either ltr (for "left to right") or rtl (for "right to left").
This attribute is OPTIONAL and, if omitted, defaults to ltr.

class

An arbitrary set of space-separated tokens.
This attribute is OPTIONAL.

value element

One or more value elements are used to provide
the value of a specific extended metadata item. A user agent
that displays metadata SHOULD choose the value with the most appropriate language from
among those available for each item element.
This child element is REQUIRED;
an item element with no
value is invalid and SHOULD be ignored.

attributes

xml:lang

A language tag as defined in BCP47 [BCP47].
This attribute is OPTIONAL.

dir

The text direction, either ltr (for "left to right") or rtl (for "right to left").
This attribute is OPTIONAL and, if omitted, defaults to ltr.

class

An arbitrary set of space-separated tokens.
This attribute is OPTIONAL.

Where text elements are used to contain (localizable) content,
further structure MAY also be provided
using div and span child elements
similar to those used in HTML.

text element

An element used to contain a particular localization of a metadata element's contents. This element has a mixed content model;
in addition to the child elements mentioned below, it may directly contain character data.

attributes

xml:lang

A language tag (as specified in BCP47 [BCP47]) indicating
the language of this particular version of the metadata element's content.
This attribute is OPTIONAL; however, for multiple text children
of a metadata element to be usefully distinguished,
they SHOULD all be tagged with appropriate different language codes.

dir

The text direction, either ltr (for "left to right") or rtl (for "right to left").
This attribute is OPTIONAL and, if omitted, defaults to ltr.

class

An arbitrary set of space-separated tokens.
This attribute is OPTIONAL.

children

div

Contains a block of text, such as a paragraph or heading.

span

Contains an inline run of text.

div element

A block-level element used, for example, to contain a paragraph.

attributes

dir

The text direction, either ltr (for "left to right") or rtl (for "right to left").
This attribute is OPTIONAL and, if omitted, defaults to ltr.

class

An arbitrary set of space-separated tokens.
This attribute is OPTIONAL.

span element

An inline element used, for example, to indicate a run of text
with a different text direction, or in a different language.

attributes

dir

The text direction, either ltr (for "left to right") or rtl (for "right to left").
This attribute is OPTIONAL and, if omitted, defaults to ltr.

class

An arbitrary set of space-separated tokens.
This attribute is OPTIONAL.

The text elements used to hold
(localizable) text for a number of the individual pieces of metadata
thus have a mixed content model consisting of text content,
div and span elements;
div elements have a mixed content model of text content,
div and span elements;
and span elements have a mixed content model of text content
and span elements.
In other words, div can contain other div elements;
span can contain other span elements;
span does not require a containing div.

Appendix A includes several examples
of the content of the metadata block.

Although the metadata block is optional,
and there is no requirement for user agents to process it
in order to render the font,
clients such as Web browsers are encouraged to provide a means
(such as a "Font Information" dialog for the current page)
for users to view the metadata included in WOFF files.
Not every client will necessarily have an appropriate context for this,
but any client that enables the user to find out about the resources used by a Web document
should consider exposing information about the fonts used, and in the case of
WOFF-packaged fonts, the metadata block is the primary source of this information.

8. Private Data Block

The WOFF file MAY include a block of arbitrary data, allowing font creators
to include whatever information they wish. The content of this data MUST NOT
affect font usage or load behavior of user agents.
User agents should make no assumptions
about the content of a private block; it may (for example) contain ASCII or
Unicode text, or some vendor-defined binary data, and it may be compressed or
encrypted, but it has no publicly defined format. Conformant user agents will
not assume anything about the structure of this data. Only the font developer or
vendor responsible for the private block is expected to understand its
contents.

The private data block, if present, MUST be the last block in the WOFF file,
following all the font tables and any extended metadata block.
The private data
block MUST begin on a 4-byte boundary in the WOFF file, with up to three null
bytes inserted as padding after any preceding metadata block
if needed to ensure this.
The end of the private data block MUST correspond to the end of the WOFF file.

Appendix A: Extended Metadata Examples

This appendix is purely informative, not a normative part of the WOFF specification.

This "dummy" metadata block illustrates the use of the metadata elements
described in section 7, including the use of multiple text
child elements to provide localized versions of certain elements.

Another example of a metadata block (reproduced by permission of Ascender Corporation).
This is dynamically generated, with the uniqueid and
licensee elements modified to be unique for each customer.

<?xml version="1.0" encoding="UTF-8"?>
<metadata version="1.0">
<uniqueid id="037d0f6b-b5e3-b841-05afa509061b" />
<vendor name="Ascender Corp" url="http://www.fontslive.com" />
<license url="http://www.fontslive.com/info/Web-fonts-eula.aspx"
id="ascender-Webfonts-eula-v1">
<text lang="en">This font software is the valuable property of Ascender
Corporation and/or its suppliers and its use by you is covered under the
terms of the Web Font license agreement between you and Ascender
Corporation. You may ONLY use this font software with the licensed Web site.
Except as specifically permitted by the license, you may not copy this font
software. If you have any questions, please contact Ascender Corp.</text>
</license>
<licensee name="FontsLive.com" />
</metadata>

Here is an example of how the div element could be used,
modified from a portion of the
XML file for Gentium Plus
which, when viewed as plain text, has paragraph formatting.

The original metadata file contained:

<description>
<text lang="en">
Gentium ("belonging to the nations" in Latin) is a Unicode typeface family
designed to enable the many diverse ethnic groups around the world who use
the Latin, Cyrillic and Greek scripts to produce readable, high-quality
publications. The design is intended to be highly readable, reasonably
compact, and visually attractive. Gentium has won a "Certificate of Excellence
in Typeface Design" in two major international typeface design competitions:
bukva:raz! (2001), TDC2003 (2003).
The Gentium Plus font family is based on the original design. It currently
comes with regular and italic face only, although additional weights are in
development.
The goal for this product is to provide a single Unicode-based font family
that contains a comprehensive inventory of glyphs needed for almost any
Roman- or Cyrillic-based writing system, whether used for phonetic or
orthographic needs, and provide a matching Greek face. In addition, there
is provision for other characters and symbols useful to linguists. This
font makes use of state-of-the-art font technologies to support complex
typographic issues, such as the need to position arbitrary combinations
of base glyphs and diacritics optimally.
(and so on)
</text>
</description>

Using the div element, this could become:

<description>
<text xml:lang="en">
<div>Gentium ("belonging to the nations" in Latin) is a Unicode
typeface family designed to enable the many diverse ethnic groups
around the world who use the Latin, Cyrillic and Greek scripts to
produce readable, high-quality publications. The design is intended
to be highly readable, reasonably compact, and visually attractive.
Gentium has won a "Certificate of Excellence in Typeface
Design" in two major international typeface design
competitions: bukva:raz! (2001), TDC2003 (2003).</div>
<div>The Gentium Plus font family is based on the original design.
It currently comes with regular and italic face only, although
additional weights are in development.</div>
<div>The goal for this product is to provide a single Unicode-based
font family that contains a comprehensive inventory of glyphs
needed for almost any Roman- or Cyrillic-based writing system,
whether used for phonetic or orthographic needs, and provide a
matching Greek face. In addition, there is provision for other
characters and symbols useful to linguists. This font makes use of
state-of-the-art font technologies to support complex typographic
issues, such as the need to position arbitrary combinations of base
glyphs and diacritics optimally.</div>
(and so on)
</text>
</description>

Appendix B: Media Type registration

This appendix registers a new MIME media type, in conformance with BCP 13 and W3CRegMedia.

Type name:

application

Subtype name:

font-woff

Required parameters:

None.

Optional parameters:

None.

Encoding considerations:

binary.

Security considerations:

Fonts are interpreted data structures that represent collections of glyph outlines, metrics and layout information for various languages and writing systems. Currently, there are many standardized font data tables that allow an unspecified number of entries, and where existing, predefined data fields allow storage of binary data with variable length. There is a significant risk that the flexibility of font data structures may be exploited to hide malicious binary content disguised as a font data component.

WOFF is based on the table-based SFNT (scalable font) format which is highly extensible and offers an opportunity to introduce additional data structures when needed. However, this same extensibility may present specific security concerns – the flexibility and ease of defining new data structures makes it easy for any arbitrary data to be added and hidden inside a font file.

WOFF fonts may contain 'hints' for the alignment of graphical elements of the glyphs with the target display pixel grid, and depending on the font technology utilized in the creation of a font these hints may represent active code interpreted and executed by the font rasterizer. Even though they operate within the confines of the glyph outline conversion system and have no access outside the font rendering machinery, hint instructions can be, however, quite complex, and a maliciously designed complex font could cause undue resource consumption (e.g. memory or CPU cycles) on a machine interpreting it. Indeed, fonts are sufficiently complex that most if not all interpreters cannot be completely protected from malicious fonts without undue performance penalties.

Widespread use of fonts as necessary component of visual content presentation warrants that a careful attention should be given to security considerations whenever a font is either embedded into an electronic document or transmitted alongside media content as a linked resource.

WOFF uses gzip compression. The WOFF header contains the uncompressed length of each compressed table. Applications may therefore constrain the size of memory buffer allocated for decompression and may stop writing if a maliciously crafted WOFF file in fact contains more data than is indicated.

WOFF does not provide privacy protections internally; if needed, these should be provided externally.

WOFF has a private data block facility, which may contain
arbitrary binary data. WOFF does not provide a means to access
this, or to execute any code contained therein. WOFF
requires that
the content of this block not affect font rendering in any way.

The signature field in the WOFF header MUST contain the "magic number" 0x774F4646

File extension(s):

woff

Macintosh file type code(s):

(no code specified)

Macintosh Universal Type Identifier code:

org.w3c.woff

Fragment Identifiers

none.

Person & email address to contact for further information:

Chris Lilley (www-font@w3.org).

Intended usage:

COMMON

Restrictions on usage:

None

Author:

The WOFF specification is a work product of the World Wide Web Consortium's WebFonts Working Group.

Change controller:

The W3C has change control over this specification.

Appendix C: Changes

The following changes have been made, relative to the
27 July 2010 First Public Working Draft. No new features have been added, except for optional enhancements to the metadata format; the remaining changes are clarifications and corrections to existing features.

Clarified that WOFF is a font packaging or wrapper format, not a new font format as such.

Clarified padding and byte-alignment requirements throughout

Preferred the term 'input font' rather than 'original file' to describe
the font which is converted to WOFF

Clarified that any subsetting, checksum-correction, or DSIG invalidating changes prior to WOFF conversion are out of scope for the WOFF specification.

Clarified meaning of totalSfntSize.

Defined what is meant by a well formed input font.

Clarified meaning of 'invalid metadata' - must be well-formed, compressed, and conform to the schema.

Clarified which elements and attributes in the XML are required;
for elements, clarified their required parents.

Clarified that the id attribute is not of type ID in the XML sense

Added link to a RelaxNG grammar, which tries to express the same constraints as the prose in a machine-readable manner. The prose is normative in case of any difference.

Some re-ordering of text to group related assertions or to improve readability; in particular, the best practices were previously an appendix and are now integrated into the main body of the specification.

Added this Changes appendix.

The following changes were made as a result of Last Call:

Language attributes now reference BCP47, and use xml:lang.

Added optional div and span elements that can be used to provide structure within metadata text.

Added dir and class attributes to metadata elements.

Removed summary of conformance requirements (duplicated material from the main body of the specification).

Somewhat rearranged and clarified description of the metadata format.

Noted that same-origin requirements are at risk, in the expectation that CSS3 Fonts will handle this instead.

Mention the need to compute the binary search fields when reconstructing an sfnt header.

Require that metadata be encoded in UTF-8, rather than allowing either UTF-8 or UTF-16.

A color-coded diff between the editors draft used to prepare the Last Call Working Draft, and the editors draft used to prepare the Candidate Recommendation, is available.

The following changes were made after publication of the Candidate Recommendation:

Removed (previously at-risk) text specifying same-origin requirements
for loading WOFF fonts, and CORS mechanism to relax the restriction,
as the CSS WG agreed to include this in CSS3 Fonts
as part of the specification of the @font-face rule.

Moved CSS3-Fonts from normative to informative section, due to removal of at-risk items.

Corrected erroneous use of MUST in a general introductory statement

A color-coded diff between the editors draft used to prepare the Candidate Recommendation, and the editors draft used to prepare the Proposed Recommendation, is available.

The following changes were made after publication of the Proposed Recommendation:

The security considerations section of the Media Type Registration appendix was updated to point into the body of the specification,
alerting the reader to the private data block and indicating that WOFF does not provide a mechanism to execute any binary code that might be
contained therein. This change was made at the request of the IANA Expert Reviewer.